Because the use of environmentally harmful pesticides such as DDT is being phased out, agriculturists are turning increasingly to organophosphorous (OP) pesticides to protect their crops. In California, we are already seeing one result of this change: an increasing incidence of OP intoxication among agricultural field workers consequent upon their exposure to OP containing foliage residues. We have undertaken studies in both the laboratory and the agricultural workplace (fields, orchards, vineyards) designed to identify those factors of pesticide application, residue alteration, worker exposure and biochemical consequences which contribute to OP poisoning. We are seeking to develop effective strategies to modify those factors which are significant contributors to worker hazard.